1. Field of the Invention
The present invention relates to a holey fiber and a method of manufacturing the same.
2. Description of the Related Art
A holey fiber is an optical fiber having air holes arranged in a periodic manner in a cladding region. The cladding region surrounds a core region. The cladding region has reduced average refractive index because of the presence of the air holes so that a light passes almost entirely through the core region because of the total reflection of the light.
Because the refractive index of holey fibers can be controlled by controlling various parameters of the air holes, the holey fibers can realize unique properties that can not be realized in the other optical fibers such as endlessly single mode (ESM) and anomalous dispersion at a short wavelength. The ESM means that a cut-off wavelength is not present and a light is transmitted in a single mode at all wavelengths. With the ESM, it is possible to realize an optical transmission at a high transmission speed over a broadband. For example, a result of an experiment of a dispersion-managed soliton transmission at a transmission speed of 10 Gb/s by forming an optical path of 100 kilometers by combining the holey fiber and a dispersion compensating optical fiber is disclosed in K. Kurokawa, et al., “Penalty-Free Dispersion-Managed Soliton Transmission over 100 km Low Loss PCF”, Proc. OFC PDP21 (2005).
For realizing long-haul transmission, it is necessary that holey fibers have low transmission loss. For example, a holey fiber with low transmission loss of 0.28 dB/km is disclosed in K. Tajima, et al., “Low water peak photonic crystal fibers”, ECOC'03 PD Th4.16 (2003).
Generally, a long optical fiber is produced by fusion splicing short optical fibers. Specifically, an end surface of one optical fiber is brought closer to an end surface of another optical fiber and then arc discharge is generated near those end surfaces whereby the optical fibers are fusion-spliced by the heat generated in the arc discharge.
However, air holes at the spliced portions may collapse due to the heat employed during fusion splicing. If the air holes collapse, the structure of the holey fiber is disturbed and it is difficult to confine light in the core region so that confinement loss increases.
One approach could be to repeatedly perform short-time discharging at a discharge intensity that does not cause collapsing of the air holes. This approach is not only time consuming but it yields a spliced portion with weaker mechanical strength.